In prior art nuclear or scintillation cameras, the vertical travel of a detector or camera has been achieved either by counterbalancing the detector about a pivot or a motor driven screw jack. This causes problems in various areas of normal clinical operations including the possibility of varying the total weight of the detector, raising or lowering the detector and maintaining the focus of the collimator at the same point. The ability to perform complex motions around a patient and view a constant slice of the patient is compromised, along with the precision and reproduceability of the motions.
While such scintillation camera systems have existed for about two decades now, performing to a greater or lesser degree satisfactorily, the advances and resolutions in newer systems have created greater demands in precision alignment between the camera and the patient support.
In general, all known nuclear camera systems, whether or not including emission computed tomography (ECT) capability, feature a counterbalanced detector, with an inherent flexure of the structure and a variable viewing point in the patient due to the radius from the pivot to the detector, or a toe or forward projecting structure to stabilize the medical diagnostic positioner. The systems inherently suffer flexure due to the permissible dimensions of the structural sections and high concentrations of structural loadings, leading to inaccuracies in reproducible positioning. The loss of resolution and contrast of the imaging device, the scintillation camera detector head, arises from mechanical flexure in the rotating cantilever structure supporting the scintillation detector or camera head and from a lack of position alignment between the bed and the detector head, particularly during rotation of the camera head. A nuclear camera system capable of both whole body static imaging as well as emission computed tomography or ECT, is the Gemini system available from General Electric Corporation, Milwaukee, Wis., and described in U.S. Pat. No. 4,651,007 (Perusek et al.). U.S. Pat. Nos. 4,645,933 (Gambini et al.) and 4,692,625 (Hanz et al.) also describe medical diagnostic detector support systems having rotating cantilevered structures.
In the prior art nuclear or scintillation cameras, the exchange and storage of collimators has been accomplished by movements of the gantry and manually exchanging the collimators. A collimator for a nuclear camera is a nuclear radiation absorbing and focussing screen having a mass between 10 and 100 kilograms. The collimators for nuclear cameras have an array of parallel holes which provide the one to one correspondence between the emission of the pattern of radiation from the patient to the pattern of individual detectors of the detector crystal. The collimators are usually made of lead and have particular characteristics most suited to the patient study and the energy of emission of the radio-pharmaceutical agent ingested by the patient. This defines that the collimators will not be of the same weight, if they encompass the energy range and have the optimum geometry for the particular application.
Previously, collimators were stored on individual trolleys or a storage rack. In the former case, the trolleys are positioned under the detector head of the scintillation camera and the detector head is lowered onto the collimator and the collimator is fixed to the detector head by bolts or similar means. In the latter case, a mobile trolley lifts the collimator from the rack, the trolley is moved to the detector head where it is lowered onto the detector and fixed by bolts or similar means. Both systems function in a satisfactory degree to a greater or lesser extent.
More recently, automatic collimator changers for scintillation cameras have been proposed which operate on a swivel exchange mechanism for exchanging the collimators. U.S. Pat. Nos. 3,982,133 (Jupa et al.), 4,109,155 (Tschunt et al.) and 4,129,784 (Tschunt et al.) are examples of such collimator exchangers.